At present, a split placement mode is adopted for LEDs, P-channel Metal Oxide Semiconductor (P-MOS) transistors and an LED driving circuit during the design of a unit board of an LED display. As shown in FIG. 1b: LED particles in FIG. 1b are four-pin Red/Green/Blue (R/G/B) common-anode three-in-one LEDs, pins 1 are common anodes, and pins 2/3/4 are cathodes of the R/G/B LEDs respectively; and one of control ports of an external display driving circuit 30′ is a constant current control signal output port, the other of the control ports is a line power supply control port, and the constant current control signal output port is matched with the line power supply control port to realize the display work of an LED array.
FIG. 1a to FIG. 1c are split placement diagrams of an LED driving circuit for common-anode three-in-one LED particles in related art. As shown in FIG. 1a, the LED driving circuit includes three logic circuits and corresponding constant current channel groups, i.e. LED driving control circuits for controlling R/G/B display in the LED unit board respectively, and the three integrated circuits have the same internal architecture, and drive the display of the LED array under the control of the external display driving circuit 30′. A current LED driving circuit includes multiple independent constant current logic components forming a constant current array; each constant current logic component consists of a constant current input end, a constant current output end and a constant current control end, the constant output ends of the constant current array are connected with an external pin GND of the LED driving circuit; the constant current array is controlled by the internal logic circuits of the LED driving circuit in a unified way to realize the ordered work of each independent constant current logic component and control the display of external LEDs; each internal logic circuit also includes two parts, i.e. an LED driving circuit input signal port and an output signal port, wherein the input signal ports are connected to the constant current control signal output port of the external display driving circuit 30′, and the output signal ports are used for cascading input signal ports of an LED driving circuit of the next stage or are idled; and P-MOS components shown in FIG. 1a are controlled by the line power supply control port to realize line-by-line power supply control over the LED array.
The LED unit board consists of an LED matrix with M lines and N columns, anodes of the LEDs in a single line are interconnected to drains of the P-MOS transistors, and a common cathode of basic colors of the LEDs in a single column is interconnected to a constant current input end of the corresponding LED driving control circuit; sources of the P-MOS transistors are connected to a power supply end VCC, and gates of the P-MOS transistors are connected to the line power supply control port; and under the control of the display driving circuit 30′, the drain of a certain P-MOS transistor is switched on to supply power to the anodes of the LEDs in the corresponding line, the constant current control signal output port controls the logic circuits of the LED driving circuit to control the ordered conduction of the constant current array and realize the ordered conduction of the current of the LEDs in the line to GND to realize the ordered switching-on of the LEDs.
From the above, the P-MOS transistors, the LED driving circuit and the display driving circuit 30′ are independently encapsulated electronic components, and a Printed Circuit Board (PCB) area occupied by the P-MOS transistors, the LED driving circuit and the display driving circuit 30′ for the LED array display of a certain resolution under the conditions of a certain scanning mode and a certain P-MOS transistor load is a fixed value, that is, the PCB area occupied by the components is a fixed value, which inevitably brings the problems of low refresh rate and high design difficulty during application to a control mode of a high-density LED display.
In addition, FIG. 2a to FIG. 2c are split placement circuit diagrams of an LED driving circuit for 6-pin R/G/B three-in-one LEDs in related art. Wherein, an anode of each 6-pin R/G/B three-in-one LED in FIG. 2b has three pins, i.e. 1, 2 and 3 respectively, corresponding to internal R/G/B anodes respectively, and a cathode of each 6-pin R/G/B three-in-one LED has three pins, i.e. 4, 5 and 6 respectively, corresponding to internal R/G/B cathodes respectively; the LED unit board consists of an LED matrix with M lines and N columns, the anodes of the LEDs in each line are interconnected to the drains of the P-MOS transistors, and a common basic color cathode of the LEDs in each column is interconnected to the input end of the LED driving circuit; the sources of the P-MOS transistors are connected to the power supply end VCC, the gates of the P-MOS transistors are connected to a power supply control logic part of the display driving circuit 30′, and the drains of the P-MOS transistors are the anodes of a group of LEDs (LEDs in a single line in FIG. 2b, the group is not purely defined into a line actually) connected to the LED unit board; the control end of the LED driving circuit is connected with a branch of an LED driving circuit control part, and driving current for switching on the LEDs flows through the input end of the LED driving circuit and the output ends of the LED driving control circuits to reach the GND from the cathodes (pins 4, 5 and 6) of the LEDs; and the display driving circuit 30′ includes a line power supply control logic part and the LED driving circuit control part, and under the control of the display driving circuit 30′, the display work of the LED unit board is realized.
FIG. 3a to FIG. 3c are split placement circuit diagrams of an LED driving circuit for R/G/B independent LEDs in related art. As shown in FIG. 3b, an anode of an R/G/B independent LED particle is pin 1, a cathode of the R/G/B independent LED particle is pin 2, and R/G/B are welded in parallel to form a full-color pixel during application; the LED unit board consists of an LED matrix with M lines and N columns, the anodes of the LEDs in each line are interconnected to the drains of the P-MOS transistors, and the common basic color cathode of the LEDs in each column is interconnected to the input end of the LED driving circuit; the sources of the P-MOS transistors are connected to the power supply end VCC, the gates of the P-MOS transistors are connected to the power supply control logic part of the display driving circuit 30′, and the drains of the P-MOS transistors are connected to the anodes of a group of LEDs (LEDs in a single line in FIG. 3b, the group is not purely defined into a line actually) of the LED unit board; the control end of the LED driving circuit is connected with a branch of an LED driving circuit control part, and the driving current for switching on the LEDs flows through the input end of the LED driving circuit and the output ends of the LED driving control circuits to reach the GND from the cathodes (pins 2) of the LED particles; and the display driving circuit 30′ includes a line power supply control logic part and the LED driving circuit control part, and under the control of the display driving circuit 30′, the display work of the LED unit board is realized.
From the above, the R/G/B LEDs have different working voltages, wherein a typical working voltage of R LEDs is 1.8-2V, and typical working voltages of G/B LEDs are 3.4-3.6V, so that output voltages of the P-MOS transistors must be higher than the sum of the typical voltages of the G/B LEDs and a typical constant current voltage of the LED driving circuit to ensure that working voltages of the G/B LEDs are normal. Thus, voltage differences of the R LEDs relative to the G/B LEDs are applied to the LED driving circuit to generate heat for dissipation, which causes high power consumption of the LED display.
For the problems of large PCB area occupied by the control circuits, low refresh rate and high power consumption of the LED display in related art, there is yet no effective solution.